There’s a huge amount of attention paid to the air temperature 6ft off the ground all around the continents of the world. And there’s an army of bloggers busy re-analyzing the data.

It seems like one big accident of history. We had them, so we used them, then analyzed them, homogenized them, area-weighted them, re-analyzed them, wrote papers about them and in so doing gave them much more significance than they deserve. Consequently, many people are legitimately confused about whether the earth is warming up.

I didn’t say land surface temperatures should be abolished. Everyone’s fascinated by their local temperature. They should just be relegated to a place of less importance in climate science.

Problems with Air Surface Temperature over Land

If you’ve spent any time following debates about climate, then this one won’t be new. Questions over urban heat island, questions over “value-added” data, questions about which stations and why in each index. And in journal-land, some papers show no real UHI, others show real UHI..

One of the reasons I posted the UHI in Japan article was I hadn’t seen that paper discussed, and it’s interesting in so many ways.

The large number of stations (561) with high quality data revealed a very interesting point. Even though there was a clear correlation between population density and “urban heat island” effect, the correlation was quite low – only 0.44.

Lots of scatter around the trend:

Estimate of actual UHI by referencing the closest rural stations - again categorized by population density

This doesn’t mean the “trend” wasn’t significant, as the result had a 99% confidence around it. What it meant was there was a lot of variability in the results.

The reason for the high variability was explained as micro-climate effects. The very local landscape, including trees, bushes, roads, new buildings, new vegetation, changing local wind patterns..

Interestingly, the main effect of UHI is on night-time temperatures:

Temperature change per decade: time of day vs population density

Take a look at the top left graphic (the others are just the regional breakdown in Japan). Category 6 is the highest population density and category 3 the lowest.

What is it showing?

If we look at the midday to mid-afternoon temperatures then the average temperature change per decade is lowest and almost identical in the big cities and the countryside.

If we look at the late at night to early morning temperatures then average change per decade is very dependent on the population density. Rural areas have experienced very little change. And big cities have experienced much larger changes.

Night time temperatures have gone up a lot in cities.

A quick “digression” into some basic physics..

Why is the Bottom of the Atmosphere Warmer than the Top while the Oceans are Colder at the Bottom?

The ocean surface temperature somewhere on the planet is around 25°C, while the bottom of the ocean is perhaps 2°C.

Ocean temperature vs depth, Grant Bigg, Oceans and Climate (2003)

The atmosphere at the land interface somewhere on the planet is around 25°C, while the top of the troposphere is around -60°C. (Ok, the stratosphere above the troposphere increases in temperature but there’s almost no atmosphere there and so little heat).

Typical temperature profile in the troposphere

The reason why it’s all upside down is to do with solar radiation.

Solar radiation, mostly between wavelengths of 100nm to 4μm, goes through most of the atmosphere as if it isn’t there (apart from O2-O3 absorption of ultraviolet). But the land and sea do absorb solar radiation and, therefore, heat up and radiate longwave energy back out.

See the CO2 series for a little more on this if you wonder why it’s longwave getting radiated out and not shortwave.

The top of the ocean absorbs the sun’s energy, heats up, expands, and floats.. but it was already at the top so nothing changes and that’s why the ocean is mostly “stratified” (although see Predictability? With a Pinch of Salt please.. for a little about the complexity of ocean currents in the global view)

The very bottom of the atmosphere gets warmed up by the ground and expands. So now it’s less dense. So it floats up. Convective turbulence.

This means the troposphere is well-mixed during the day. Everything is all stirred up nicely and so there are more predictable temperatures – less affected by micro-climate. But at night, what happens?

At night, the sun doesn’t shine, the ground cools down very rapidly, the lowest level in the atmosphere absorbs no heat from the ground and it cools down fastest. So it doesn’t expand, and doesn’t rise. Therefore, at night the atmosphere is more stratified. The convective turbulence stops.

But if it’s windy because of larger scale effects in the atmosphere there is more “stirring up”. Consequently, the night-time temperature measured 6ft off the ground is very dependent on the larger scale effects in the atmosphere – quite apart from any tarmac, roads, buildings, air-conditioners – or urban heat island effects (apart from tall buildings preventing local windy conditions)

There’s a very interesting paper by Roger Pielke Sr (reference below) which covers this and other temperature measurement subjects in an accessible summary. (The paper used to be available free from his website but I can’t find it there now).

One of the fascinating observations is the high dependency of measured night temperatures on height above the ground, and on wind speed.

Micro-climate and Macro-climate

Perhaps the micro-climate explains much of the problems of temperature measurement.

But let’s turn to a thought experiment. No research in the thought experiment.. let’s take the decent-sized land mass of Australia. Let’s say large scale wind effects are mostly from the north to south – so the southern part of Australia is warmed up by the hot deserts.

Now we have a change in weather patterns. More wind blows from the south to the north. So now the southern part of Australia is cooled down by Antarctica.

This change will have a significant “weather” impact. And in terms of land-based air surface temperature we will have a significant change which will impact on average surface temperatures (GMST). And yet the energy in the climate system hasn’t changed.

Of course, we expect that these things average themselves out. But do they? Maybe our assumption is incorrect. At best, someone had better start doing a major re-analysis of changing wind patterns vs local temperature measurements. (Someone probably did it already, as it’s a thought experiment, there’s the luxury of making stuff up).

How much Energy is Stored in the Atmosphere?

The atmosphere stores 1000x less energy than the oceans. The total heat capacity of the global atmosphere corresponds to that of only a 3.2 m layer of the ocean.

So if we want a good indicator – a global mean indicator – of climate change we should be measuring the energy stored in the oceans. This avoids all the problems of measuring the temperature in a highly, and inconsistently, mobile lightweight gaseous substance.

Right now the ocean heat content (OHC) is imperfectly measured. But it’s clearly a much more useful measure of how much the globe is warming up than the air temperature a few feet off the ground.

If the primary measure was OHC with the appropriately-sized error bars, then at least the focus would go into making that measurement more reliable. And no urban heat island effects to worry about.

How to Average

There’s another problem with the current “index” – averaging of temperatures, a mix of air over land and sea surface temperatures. There is a confusing recent paper by Essex (2007), see the reference below, just the journal title says it’s not for the faint-hearted, which says we can’t average global temperatures at all – however, this is a different point of view.

There is an issue of averaging land and sea surface temperatures (two different substances). But even if we put that to one side there is still a big question about how to average (which I think is part of the point of the confusing Essex paper..)

Here’s a thought experiment.

Suppose the globe is divided into 7 equal sized sections, equatorial region, 2 sub-tropics, 2 mid-latitude regions, 2 polar regions. (Someone with a calculator and a sense of spherical geometry would know where the dividing lines are.. and we might need to change the descriptions appropriately).

Now suppose that in 1999 the average annual temperatures are as follows:

Equatorial region: 30°C

Sub-tropics: 22°C, 22°C

Mid-latitude regions: 12°C, 12°C

Polar regions: 0°C, 0°C

So the “global mean surface temperature” = 14°C

Now in 2009 the new numbers are:

Equatorial region: 26°C

Sub-tropics: 20°C, 20°C

Mid-latitude regions: 12°C, 12°C

Polar regions: 5°C, 5°C

So the “global mean surface temperature” = 14.3°C – an increase of 0.3°C. The earth has heated up 0.3°C in 10 years!

After all, that’s how you average, right? Well, that’s how we are averaging now.

But if we look at it from more a thermodynamics point of view we could ask – how much energy is the earth radiating out? And how has the radiation changed?

After all, if we aren’t going to look at total heat, then maybe the next best thing is to use how much energy the earth is radiating to get a better feel for the energy balance and how it has changed.

Energy is radiated proportional to σT4, where T is absolute temperature (K). 0°C = 273K. And σ is a well-known constant.

Let’s reconsider the values above and average the amount of energy radiated and find out if it has gone up or down. After all, if temperature has gone up by 0.3°C the energy radiated must have gone up as well.

What we will do now is compare the old and new values of effective energy radiated. (And rather than work out exactly what it means in W/m2, we just calculate the σT4 value for each region and sum).

1999 value = 2714.78 (W/arbitrary area)

2009 value = 2714.41 (W/arbitrary area – but the same units)

Interesting? The “average” temperature went up. The energy radiated went down.

The more mathematically inclined will probably see why straight away. Once you have relationships that aren’t linear the results doesn’t usually change in proportion to the inputs.

Well, energy radiated out is more important in climate than some “arithmetic average of temperature”.

When Trenberth and Kiehl updated their excellent 1997 paper in 2008 the average energy radiated up from the earth’s surface was changed from 390W/m2 to 396W/m2. The reason? You can’t average the temperature and then work out the energy radiated from that one average (how they did it in 1997). Instead you have to work out the energy radiated all around the world and then average those numbers (how they did it in 2008).

Conclusion

Measuring the temperature of air to work out the temperature of the ground is problematic and expensive to get right. And requires lot of knowledge about changing wind patterns at night.

And even if we measure it accurately, how useful is it?

Oceans store heat, the atmosphere is an irrelevance as far as heat storage is concerned. If the oceans cool, the atmosphere will follow. If the oceans heat up, the atmosphere will follow.

And why take a lot of measurements and take an arithmetic average? If we want to get something useful from the surface temperatures all around the globe we should convert temperatures into energy radiated.

48 Responses

But as previously, you have a way o making your points easy to comprehend. I have a Q… ok so i know soil temps(sub surface, a few inches) are relatively constant depending on season… but what warms them faster than anything is rain! Hot days or cold days take a few days to move them a few degree’s, with rain it happens more or less instantly. So the thermal transferring from rain to say oceans(id assume the same, but not same extent, due albedo and mixing o depth with oceans) or soil, is that just really juggling energy transfer, or would it increase it?

Because im “guessing”(i can do this…because im not a scientist) that if that thermal energy is left in the atmosphere more would be lost in outward radiation? Or would more be absorbed through long wave with that heat still in the atmosphere?

Basically, would rain effect energy transfer from atmosphere to soil and oceans?

P.S. thanks for answers to past Q’s, and to this one if yer know…and undoubtedly future Q’s

“Average temperature” is a concept with no physical meaning. It could still have its uses, but the lack of physical meaning has a huge practical implication: you have no physical way of telling whether you’re calculating it right.

Heat is a concept with physical meaning. It’s energy. Therefore it participates in the conservation of energy. You can check that your values for ocean heat content are correct, by checking the energy that flows in and flows out, and that the difference is equal to the change in your value for ocean heat content.

There is no similar check for global average temperature. If there were, I think we would have heard of it by now.

Assuming you can calculate or measure the energy radiated to space – 396 W/sqm for now, then you can also calculate an effective black-body temperature equivalent – the ‘true’ temperature of the earth.

Of course, the earth is not a black body, neither for radiation to space in the first instance, nor for the purposes of calculating the equivalent temperature.

So what are the non-black body corrections required for the initial calculation 396W/sqm? And what are the corrections for the equivalent temperature calculation? And do they cancel out (I think not due to the non-linearity issue) ?

The emissivity of the earth’s surface for longwave energy is close to 1, and assuming it’s 1 gives “pretty good” results (hope you didn’t mind the over-complicated technical analysis there..)

Do they cancel out? We can’t assume so if the emissivity varies enough across the globe and the temperature also varies enough.

A little comment from Kiehl and Trenberth (2008):

“The surface emissivity is not unity except perhaps in snow and ice regions, and it tends to be lowest in sand and desert regions, thereby slightly offsetting effects of the high temperatures on longwave (LW) upwelling radiation. It also varies with spectral band (see Chédin et al. 2004 for discussion). Wilber et al. (1999) estimate the broadband water emissivity as 0.9907 and compute emissions for their best estimated surface emissivity versus unity. Differences are up to 6 W m-2 in deserts, and can exceed 1.5 W m-2 in barren areas and shrublands.”

His reference, A.C. Wilber “Surface Emissivity Maps for use in Satellite Retrievals of Longwave Radiation” (1999) – introduces the subject by saying:

“Recent measurements of spectral reflectances of surface materials have clearly demonstrated that surface emissivities deviate considerably from unity, both spectrally and integrated over the broadband..”

Then the graphs are mostly not far off 1. I’ll take a closer look, as this looks like an interesting paper, and a good question that you asked.

I shall, so rain can shift soil temps a few degrees a day(whatever temp the rain is, the soil will be very similar that day) So it can raise it from say 8 C too 13C in a day, or drop it five degrees in a day.

Now obviously the thermal energy o the rain is approx the same as the air temp at the time. So i assume its transferring thermal energy from the atmosphere to the soil or soil to the atmosphere(depending whether negative or positive effect at time) at a greatly accelerated rate than what would happen on a fine day.

So my Q is that moving this energy between lower atmosphere and soil/oceans(assuming on the oceans) in an accelerated way, is that going to effect long wave radiation transfer in a significant way? With the LW being relative to T^4 from the atmosphere downwards, would transferring “heat” energy through the rain effect over all energy, or would the transfer be equal to if the energy stayed in the atmosphere but got transferred through LW radiation?

Im sorry if this is coming across a lil confusing, truth is im confusing myself a lil bit… but im kinda assuming longwave wouldnt conduct as well from below surface in the soil as in the atmosphere, or vice versa… Now my heads hurting.

One way this occurs is latent heat. Water is evaporated on, or near to, the earth’s surface – this requires (absorbs) energy – and then higher up in the atmosphere the water vapor condenses to liquid and releases the latent heat.

Radiation is in proportion to T^4. Irrespective of how much extra energy is stored – water, ice, soil and shrubs at 15’C will radiate at 390W/m^2.

If they have less heat capacity then that radiation will “drain” the heat out faster and lower the temperature. Unless something is replenishing the heat.

If latent heat removal via water-water vapor lowers the surface temperature then it will reduce the longwave radiation from the earth’s surface.

Because the climate system is in constant change and convection, latent heat and radiation all move heat around, it’s hard to completely answer the question.

A great resource for a quick overview of climate basics is the Chapter 1 of the TAR (Third Assessment Report 2001) of the IPCC. Really nice introduction on climate basics. Recommended. http://www.ipcc.ch

Another interesting, thought provoking post. Can we conclude that a change in a higher temperature means more energy change than the same change in a lower temperature? Even though the two polar regions had a +5 increase, the decrease in the higher equatorial and subtropics temperature meant more in energy change?

I guess that follows from the math if indeed energy varies as a power of 4 with absolute temp.

(lowertemp+x)**4 – lowertemp**4 < (highertemp+x)**4 – highertemp**4

For example for a temperature of 3kelvin, or just the number 4 for that matter, and forget the constant,

I guess that since thermal pyrometry uses a broad spectrum sensor the emissivity is calculated assuming some form of black/grey-body spectral curve based on the reference temperature given for each material.

The pyrometry figures generally match the relationship shown in your graphs. What is not shown in your graphs is the figures for plowed fields – or for other agricultural surfaces with potentially lower emissivity. Of course a plowed field is only plowed for a bit of the time. Over longer periods perhaps crops have much higher emissivities and so cancel out the lower emissivity of bare fields?

I have never liked the idea of Global average tempertures and when you see how Hansen and Lebedev ‘invented’ them with their 1987 paper it is a wonder it has gained so much traction.

The thermometer was designed to take the temperature of the micro climate immediately around it-nothing more. If the area round the thermometer changes in nature it is still measuring that micro climate but we are now comparing apples and oranges.

When, as very frequently happens, the thermometer is moved many miles away to a completely different environment -say to an airport-even without introducing UHI into the equation it is clear the micro climate now being measured is so didfferent that the apples that became oranges have now become pineapples.

How anyone can take this very local information and glue it together with thousands of others from around the world -all of which have changed in numbers,location and circumstances- and believe it forms any sort of serious and scientific measure is beyond me.

Obiously satellite measurements since 1979 introduce a new factor although they have their own problems and only serves to introdce yet more complexity.

You said;

“At best, someone had better start doing a major re-analysis of changing wind patterns vs local temperature measurements. (Someone probably did it already, as it’s a thought experiment, there’s the luxury of making stuff up).”

There are a variety of wind studies correlating changing temperatures with direction-Hubert Lamb did a number dating back centuries. It seems clear that a predominantly easterly helped cause the LIA in Northern Hemispheres and predominant westerlies/sountherlies helped cause the MWP.

I am doing a post on it myself but I need some graphics to illustrate the point which are currently beyond my programs (and my graphic skills!)

That was a great article.
Just now, the hockey team is being picked apart for hiding details, but once that examination is over, perhaps we can take note of the crux of the matter – as tonyb also reckons.

Let them measure the temperature of a toe, an ear and a belly button and average them to equal horrible fevers on their own dime. Is it relevant whether they practice numerology by the book or not? Scholarly climaturgical debate over the authenticity of the gospel graphics actually appears to validate the mythology.

And a point that (in a different way) many less in the thick of the “climate change movement” have made. No one experiences the average. And why pick temperature? What about humidity? And so on.

The more important point for this analysis is that GMST is used a “danger index” proxy, in that it indicates the heat that is being accumulated.

But an arithmetic mean of temperature doesn’t correctly assess energy accumulation, especially as air is light and ephemeral and the randomness of its temperature 6ft above the ground may be a problem we never actually overcome..

In fact, only energy accumulation correctly assesses “energy accumulation”, but, at the least, energy radiated by the surface should be next in the queue.

It’s not really that controversial, but like a supertanker changing direction, everyone carries on doing what they’ve been doing..

Having grown up in a farming community corn fields are hotter then grazing fields.

The amount of adjustments that would have to be made to accurately compare annual surface temperature 6 feet off the ground is infinite. One would have to have the complete historical record of farming, construction and any other variable, for just 1 thermometer.

Even if we adjust for population maybe someone then does another study on rural temperature stations and finds that there is a vegetation growth effect due to temperature so we have to then correct the temperature in stations by a factor relating to temperature! and proximity of nearby vegetation..

Well, once we have finally properly corrected for UHI perhaps we will find we can only correct for temperature by using temperature. More work for an army of unpaid statisticians..

scienceofdoom,
This is a very interesting post and thread.
It seems that processing data, like processing food, runs the risk of delivering poor nutirional value/weak substance- or worse.
As I read your latest comment, the question comes to mind:
What is the value of focusing on anomalies?

Jerry: “Assuming you can calculate or measure the energy radiated to space – 396 W/sqm for now, then you can also calculate an effective black-body temperature equivalent – the ‘true’ temperature of the earth.”

You can, but it doesn’t tell you much about the surface.

The earth’s atmosphere is almost opaque in the thermal IR. If you were an alien with eyes that saw in the thermal IR, instead of the human visible, the earth would look like a featureless, glowing ball, with a “surface” high in the atmosphere. This is the “equivalence layer.” The energy emitted to space from the equivalence layer is whatever it has to be to maintain equilibrium with the energy absorbed from the Sun.

If greenhouse gases are added to the atmosphere then, assuming energy absorbed doesn’t change, the energy emitted doesn’t change either. The equivalence layer just moves higher in the atmosphere, since the atmosphere is even more opaque due to the added gas. (IIRC, the equivalence layer is at about 5km, and doubling CO2 would move it up another 170 meters.) The temperature at the equivalence layer doesn’t change!

“If we look at the late at night to early morning temperatures then average change per decade is very dependent on the population density. Rural areas have experienced very little change. And big cities have experienced much larger changes.”

Data is data until it’s adjusted. Then it is ‘derived product’ which may or may not be data.

If I were to take 20 vocal tracks and average them repeatedly in subsets and then average the subsets- nobody would let me get away with calling it a Chorale, eh?
It would be mud.

Raw data is data.
Averaging the temperature of Tahoe with the temperature of Tampa is to render raw data meaningless.
Averaging a month of those makes thicker mud.
You can not locate a signal or hear a voice when you mix it to mud.

Anyway, degrees are not watts.

All the weather data is good weather data, though. City temps are valid city temps; rural temps are valid rural temps.
What’s needed and what nobody has done is to create the software to view the raw data or any filtered subset, plotted at its station location on a map that is animated so you can examine it at any geographic or temporal scale and compare it with other views of the data.

This is the basic tool required to discover what use can be made of this data. The data can only stand on its own when it’s given the stage. Then it can speak truth rather than perform like an organ grinder’s pet.

Scienceofdoom- you have an island of rationality in a world awash in apocalyptic cybermancy and climate clairvoyants.

Does anybody want to
1- prepare a bitmap of North America with stations located 2- on it (including pixel coordinates)…
3- gather raw data for those stations into daily samples…
write the code to parse the files and plot the raw data in color representing the raw temp…
4- plot each day of data as a frame and assemble all the frames into an animation that can be played at any speed or zoomed to either extreme of scale…
?

This is, specifically, my idea of what should be done with that sort of data as the very first step of analysis.
I’d love to know what thoughts you may brew about that.

It’s all about heat, isn’t it? I mean, if there’s any sense to be made of the term ‘global temperature’ it must really mean heat content (in some interactive locii, not inaccessible geothermal heat).

To find that, satellite radiometry can measure the global output vs solar input and determine if there’s a net gain or loss and range of equilibrium. There’s no more elegant way I can imagine.

But all that data is good.
If it were made intelligible (can you imagine what Pixar would have given for that kind of money?) the data would leap out with what it has to say.
If one station is behaving oddly- it will show.
If there are patterns or cycles- you can compare one clip to another and expect that an identical pattern in process should produce identical consequences- and if they don’t- then you know where to make an experiment or a hypothesis.

Nobody wants to examine the raw data because they only want props for a salvation show or to quibble on stage over the performance. The graphs are like the old witchdoctor’s rattles and PhD’s like big feather headdresses. There is no sense to what they are doing.

Well, as I said, I can do the code for parsing and plotting but I’m not ready to reinvent what I’m sure somebody already has somewhere. The bitmap is also a big chore that would take time to plot all the stations, but that might be undertaken in stages. I want to contribute, not run a project this size, especially when there are others far superior in resources and motivation – like who might atually get some use out of such a tool.

I’d lile to see it done because you can’t do anything with all that data until it is- and I’m not above enjoying the schadenfreude of random anonymous geeks doing for fun what a few billion can’t seem to get done by soix disant professionals.

I agree that surface temperatures are too many times removed from energy balances to be trustworthy.

There is great confusion of the use of physics in climate studies. To use the air temperature measured at 2 meters to infer the surface temperature of the ground or sea and then use it in a black or gray body formula, assumes implicitly that an equilibrium has been reached between the two surfaces. This is erroneous, most of the time there is no equilibrium;

1)Deserts and open ground. The sand or ground in the sun is much hotter than the air measured. In hot countries the ground is over 50 degrees when the air is below 40, just because of local convection.

2) the sea water is much cooler than the air by more than 10 degrees in the sun. There is also evaporation to be considered. Lets hope that in the energy balances they take the temperature of the water.

3) trade winds and general circulations last for months in certain areas. Greece, where I live, would be much hotter in the summer if it were not for northern winds blowing sometimes continuously and bringing the temperature down. The same in winter.

This one is for all those still trying to understand the topic by a day to day example.

Given:
A black metallic car is driving for 2 hours down an easy highway with an av. speed of 80mph.
It’s a lazy sunny afternoon at wintertime, so the outside temperature is -12°C.
For this purpose the car is equipped with numerous of sensors everywhere for registration of temperatures. These will be stored in records by an onboard device every minute during the trip. Basic measurement results are:
Front tiers are at 31°C and 4°C lower at the rear tiers (front wheel drive). The rims are 6°C colder then the tiers. Engine compartment is at 42°C and the engine coolant is at 90°C whereas the oil pan is at 70°C and the combustion chamber is at 350°C. There are two persons in the car. Although they prefer different seat heater settings: he prefers 25°C whereas she likes 27°C, both are fine with AC set at 22°C and both are in good health, so their body temperature is at 37°C. Apart from a couple of wine bottles the trunk is empty and at 10°C. Finally at the exhaust 32°C can be measured. Given also, all of the raw data are available.

Question:
Can you calculate a mean temperature for this 2 hour drive and if so, please explain the meaning and applicability of your result?

[Thanks to the original submitter in a German Blog, I’ve just been the translator]

[…] 6, 2010 by scienceofdoom In an earlier post – Why Global Mean Surface Temperature Should be Relegated, Or Mostly Ignored – I commented: There’s a huge amount of attention paid to the air temperature 6ft off the […]

On calculating the surface temperature from paleoclimate proxies, they usually “infill” the big spatial gaps between available proxies. How is this done? It involves models, but I’d like to know more about it. Where could I find some more information?

One example is Mann et al. 2009

“Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly”

[…] for denialism? Perhaps there is: in “Science of Doom” one can even read about “why Global Mean Surface Temperature should be relegated, or mostly ignored“. And the post about the “lunar greenhouse effect” or lack thereof explicitly […]

[…] an average temperature has a lot of issues, as explained in Why Global Mean Surface Temperature Should be Relegated, Or Mostly Ignored. However, the explanation above doesn’t rely in any way on the arbitrary construct of average […]

IMO, this is an interesting, thoughtful and completely wrong headed post. What is wrongheaded about it is illustrated by the common meme that ‘average temperature has no physical meaning’. A measurement has ‘meaning’ if it conveys information about whatever is measured, or some related system. Clearly, a data set of closely spaced, equidistributed temperature measurements around the globe would convey information about changes in one significant climate variable – temperature. As such, such a data set would have a physical meaning. It follows the average of that data set would also convey information about that variable. Not as much information, for averaging reduces information content. But real information non-the-less.

I am sure that Hansen would much rather convey the data of all the measurements he analyses rather than simply summarize it as a single number by taking an average. In fact, he has gone to great lengths to make the overall data accessible with Surface Temperature Analysis maps (which again do not convey the full information because of the use of Mercator projections, and issues of resolution). However, newpapers won’t print the full dataset, nor readers read it – so he summarizes with a single number, knowing that it does not convey all the information he has available.

So, the notion that Global Mean Surface Temperature has ‘no physical meaning’, ie, conveys no climatological information, is absurd. Whether it conveys more or less information than, say, records of glacier lengths would be an interesting point to debate. But, of course, other measures of climate (such as glacier lengths, sea ice extents, ratio of maximum to minimum temperature records, date of first flowering of plants, dates of migrations, and so on) all show a consistent record of a warming earth.

Which brings me to the actual content of the blog. ‘Science of Doom’ first suggests that the temperature records are not to be relied on because there are difficulties in the measurements. Well, granted that there are difficulties in measurement, as there are in any form of measurement. It does not follow that those difficulties overwehlm the climate signal. To check whether they do, the logic procedure is to compare the derived climate signal from the measurements (delta GMST) with other climate signals. Universally, they show a consistent story, which implies that the noise from UHI, faulty sites, and microclimates is not overwhelming the climate signal.

That is an obvious point. So obvious that failure to appreciate clearly indicates the interlocuter is seeking pretexts to avoid uncomfortable information, rather than seeking to get the best information possible.

Moving on, ‘Science of Doom’ provides us with a thought experiment. What is missing from his thought experiment is any balancing of energy flows. If cold air moves across the Australian continent from Antarctica, then warm air must be displacing that cold air in Antarctica, and warming it. So, it is not that such air movements will balance over time in the climate record. Rather, they are likely to be balanced at the same time by variations in temperature in other regions. If they are not, they represent genuine changes in global temperatures which will be detected by a global network.

Next, ‘Science of Doom’ introduces the concept of energy radiated out, which is claimed to be more important than average temperature in climate. Well, first, in the effects on us, we humans, it is air and water temperatures that concern us, not any radiation that may result from it. Second, in as much as radiation out has a long term effect on climate, it is the radiation at the top of the atmosphere that is relevant, not that at the surface. As the tropopause is not the same altitude around the world, being much closer to the surface at the poles, the radiation out is more even than across the globe than your model allows.

Worse, it is not the case that the poles are warming while the tropics are cooling. Rather, the tropics are warming, while the North Pole is warming faster. Because radiation varies with the fourth power of temperature, and because tropical temperatures are higher, it may well be that there has been a greater increase in global surface LW radiation than there has been an increase in GMST. (I don’t know that there has been.) So even if your point about radiation were valid (which it is not), you have not shown that GMST is not a reliable indicator of change in surface radiation under the circumstances that actually prevail.

This is very well written article on temperature. Very good science that is well explained in an effective manner.

I had noticed that Japan has a very strong UHI and I enjoyed the breakdown of the timing in the city vs rural. That is also what makes intuitive sense as cities (cement and brick) absorb lots of energy and then holds onto it longer than non industrial materials.

It would be nice to be able to measure the surface temperature, but UHI issues would be a nightmare. As would grass or weeds overgrowing sensors.

I tend to favor satellite, I just wish there was a longer record of it. What is available is the station data. So that is what gets used.

[…] Note 1 – The concept of an average temperature is not really needed to actually do this calculation. Averaging temperatures across different surface materials like oceans, rocks, deserts clearly has some problems – see for example, Why Global Mean Surface Temperature Should be Relegated, Or Mostly Ignored. […]

“Second, in as much as radiation out has a long term effect on climate, it is the radiation at the top of the atmosphere that is relevant, not that at the surface. As the tropopause is not the same altitude around the world, being much closer to the surface at the poles, the radiation out is more even than across the globe than your model allows.”

Tom Curtis apparently is not familiar with the standard greenhouse effect. If he would study a bit harder, he might understand that tropopause has nothing to do with magnitude of GH effect. It is well explained (Hansen 1981, Soden 2000, etc) that the magnitude of GH effect depends on “effective emission height”, which is a measure of average opacity of air in IR range. It has been established that this height is at about 6km, or well below the tropopause. Since the GH gas under question is “well mixed”, the spectroscopically relevant emission height is largely independent of geographical location and tropopause height. Combined with more-or-less the same lapse rate, the radiating “top” of atmosphere resembles the temperature pattern on the surface. This fact can be easily observed from satellites. Therefore, the construction presented by SoD in this article and its shortcoming is pretty much valid, at least with climatological accuracy.

It does not require any difficult physics or maths to immediately
understand that you can’t meaningfully talk of an average temperature
of a large body which has different parts at different temperatures.

(1) You can’t average averages (at least, not without some numerical
weighting scheme, which needs a rationale.)

(2) Temperatures are themselves averages

(3) Therefore you can’t average temperatures. QED

A little expansion.

Re: (1)

Consider a class of boys and girls. The boys height is 80 cm on average
and the girls’ height 70 cm on average. What is the average of the whole
class? Is it (80+70)/2 = 75 cm (i.e. the average of the averages)? Not likely. It depends how many boys there are and how many girls. The information given is only sufficient to establish that the average height of the class must lie between 70 and 80 cm.

Re: (2)

The temperature of a body (which has to be of a uniform temperature before
there is any meaning at all) is defined by reference to the average microcopic heat energy of the constituent particles.

Generally:

I would say that (1) is simply a common-place of statistics, and (2) is
likewise just elementary atomic theory of heat.

Before anybody tries to devise a weighting scheme for the masses and
the heat capacities of the globe, I suggest he seriously consider the problems
of devising a weighting scheme just for the room he is sitting in. How many
different temperatures would a thermometer show as it is carried around the
room and stuck at varying depths into the materials. Where does the room
begin and end? In the middle of the walls, at the interior surface of the walls
at the outer surfaces of the walls? What are the temperature gradients. Exactly
how much mass is involved for each component. Does the occupant weigh
78.5666 kg or 78.6555 kg? Is the skin of the occupant at 30 C or 27 C?
Several trillion molecules of air blew in or out of the room in the last second;
were they all at 10 C or 15 C or…?

if you are still monitoring comments on this topic, there is something else that I am curious to resolve. As I understand it, the mean temperature for each recording station is ascertained by taking Tmax and adding Tmin and dividing by 2. Can you confirm that this is correct?

The resultant mean temperature is then subjected to the further averaging torture that you mention.

However, if this is indeed the parctice, then it throws up another problem. Tmax is a moment in time, as is Tmin. If in one location the temperature is within a close proximity of Tmax or Tmin for a long period of time this will indicate a lot more heat energy at that point on earth than a similar mean where Tmin or Tmax are achieved for a short period of time. Put simply it does not seem to me that the way that average temperature is calculated is a very good proxy for heat energy.

Over and above this the global average temperature is such a blunt metric that it tells us nothing about the quality of warming or cooling. Neither on a regional or local basis, nor as to whether it is driven by higher/lower minima/maxima by night or season.